linux-kernel - Re: [patch 0/2] Immediate Values

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Message-ID: <481682D6.5010207@zytor.com>
Date:	Mon, 28 Apr 2008 19:07:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch 0/2] Immediate Values - jump patching update

Mathieu Desnoyers wrote:
> 
> Peter, do you have something like the following code in mind ?
> 

Basically, although I was suggesting using a per-site dynamic piece of 
code.  Data items may not necessarily be in registers.

> I think the main differences between the code snippet down here and the
> markers is that markers rely on the compiler to generate the stack
> setup, and have this code a little bit closer to the function than what
> I propose here, where I put the stack setup code in a "farfaraway"
> section.  Moreover, markers are much simpler than what I show here.
> And actually, markers can be deployed portably, with
> architecture-specific optimizations refined later. This has to be
> implemented all up front for any traced architecture. In addition,
> dealing with weird types like unsigned long long can become a pain.
> Also, due to fact that we are asking the compiler to put keep some
> variables live in registers, I would be tempted to embed this in a block
> controlled by an if() statement (conditional branch, like I use for the
> markers) so we don't have to pay the penality of populating the
> registers when not required if there are not live at the marker site.

We're requesting to keep them *alive*, but not necessarily in registers 
(that would be an "r" constraint.)

	-hpa
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